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W. N. Brandt - One of the best experts on this subject based on the ideXlab platform.
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The Properties and Redshift Evolution of Intermediate-Luminosity Off-Nuclear X-Ray Sources in the Chandra Deep Fields
The Astronomical Journal, 2006Co-Authors: Bret Lehmer, W. N. Brandt, Ann Hornschemeier, David M. Alexander, Franz E. Bauer, Anton M. Koekemoer, Donald P. Schneider, A. T. SteffenAbstract:We analyze a population of intermediate-redshift (z ≈ 0.05-0.3) off-Nuclear X-ray Sources located within optically bright galaxies in the Great Observatories Origins Deep Survey and Galaxy Evolution from Morphology and SEDs fields. A total of 24 off-Nuclear Source candidates are classified using deep Chandra X-Ray Observatory exposures from the Chandra Deep Field-North, Chandra Deep Field-South, and Extended Chandra Deep Field-South; 15 of these are newly identified. These Sources have average X-ray spectral shapes and optical environments similar to those observed for off-Nuclear intermediate-luminosity (LX ≥ 1039 ergs s-1 in the 0.5-2.0 keV band) X-ray objects (IXOs; sometimes referred to as ultraluminous X-ray Sources) in the local universe. This sample improves the available Source statistics for intermediate-redshift off-Nuclear Sources with LX 1039.5 ergs s-1, and it places significant new constraints on the redshift evolution of the off-Nuclear Source frequency in field galaxies. The fraction of intermediate-redshift field galaxies containing an off-Nuclear Source with LX 1039 ergs s-1 is suggestively elevated (≈80% confidence level) with respect to that observed for IXOs in the local universe; we calculate this elevation to be a factor of ≈1.9. A rise in this fraction is plausibly expected as a consequence of the observed increase in global star formation density with redshift, and our results are consistent with the expected magnitude of the rise in this fraction.
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New X-Ray Constraints on Starburst and Seyfert Activity in the Barred Spiral Galaxy NGC 1672
The Astronomical Journal, 2000Co-Authors: P. J. De Naray, W. N. Brandt, Jules P. Halpern, Kazushi IwasawaAbstract:The nearby barred spiral galaxy NGC 1672 shows dramatic starburst activity and may also host a Seyfert 2 nucleus. We present new X-ray observations that set constraints on starburst and Seyfert activity in NGC 1672. Two ROSAT HRI exposures, taken in 1992 and 1997, are used to investigate long-term variability of the known X-ray Sources and to search for new Sources of X-ray emission. We find large-amplitude (≈69%) variability from X-3, one of the off-Nuclear Sources located near an end of the galactic bar. X-3 has a peak observed 0.2–2.0 keV luminosity of ≈2.5 × 1039 ergs s-1, and it is probably a luminous X-ray binary or young supernova remnant. We do not observe variability of the Nuclear Source X-1 or the strong off-Nuclear Source X-2. Our analyses also reveal two new off-Nuclear Sources, one of which is associated with a bright region along a spiral arm, and we find evidence for large-scale diffuse X-ray emission throughout part of the disk of NGC 1672. Furthermore, we use ASCA data taken in 1995 to constrain the hard X-ray properties of NGC 1672. While the Nuclear Source X-1 is the dominant soft X-ray Source in NGC 1672, we find that the bulk of the 2–10 keV and 5–10 keV emission is spatially coincident with the off-Nuclear Source X-3, giving it an apparent 0.2–8 keV luminosity of 6 × 1039 ergs s-1. A power-law–plus–Raymond-Smith model provides an acceptable fit to the full-band ASCA spectra. We do not find any evidence for a luminous but absorbed Nuclear X-ray Source. If there is a luminous Seyfert 2 nucleus in NGC 1672, it must be obscured by a "Compton-thick" torus with a column density of 2 × 1024 cm-2.
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ROSAT PSPC and HRI observations of the composite starburst/Seyfert 2 galaxy NGC 1672
Monthly Notices of the Royal Astronomical Society, 1996Co-Authors: W. N. Brandt, Jules P. Halpern, K. IwasawaAbstract:The nearby barred spiral galaxy NGC 1672 has been observed with the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) instruments on board the ROSAT X-ray satellite. NGC 1672 is thought to have an obscured Seyfert nucleus, and it has strong starburst activity as well. Three bright X-ray Sources with luminosities 1-2 x 10(exp 40) erg/s are clearly identified with NGC 1672. The strongest lies at the nucleus, and the other two lie at the ends of NGC 1672's prominent bar, locations that are also bright in H alpha and near-infrared images. The Nuclear Source is resolved by the HRI on about the scale of the recently identified Nuclear ring, and one of the Sources at the ends of the bar is also probably resolved. The X-ray spectrum of the Nuclear Source is quite soft, having a Raymond-Smith plasma temperature of approximately equals 0.7 keV and little evidence for intrinsic absorption. The ROSAT band X-ray flux of the Nuclear Source appears to be dominated not by X-ray binary emission but rather by diffuse gas emission. The absorption and emission properties of the Sources, as well as their spatial extents, lead us to models of superbubbles driven by supernovae. However, the large density and emission measure of the Nuclear X-ray Source stretch the limits that can be comfortably accommodated by these models. We do not detect direct emission from the putative Seyfert nucleus, although an alternative model for the Nuclear Source is thermal emission from gas that is photoionized by a hidden Seyfert nucleus. The spectra of the other two X-ray Sources are harder than that of the Nuclear Source, and have similar difficulties with regard to superbubble models.
Gerd Weigelt - One of the best experts on this subject based on the ideXlab platform.
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Diffraction-limited 76mas speckle masking observations of the core of NGC 1068 with the SAO 6m telescope ?
Astronomy and Astrophysics, 1998Co-Authors: Markus Wittkowski, Yuri Balega, Thomas Beckert, Wolfgang J. Duschl, K.-h. Hofmann, Gerd WeigeltAbstract:We present the rst K-band bispectrum speckle in- terferometry of NGC1068 with an angular resolution of 76mas ( 5:5pc). This angular resolution allows us to attribute the measured flux to only one of the Nuclear Sources seen at ra- dio wavelengths. The observed decreasing visibility function suggests that the dominant central core is probably not an un- resolved point Source, but slightly resolved with a FWHM di- ameter of 30mas 2pc for an assumed Gaussian intensity distribution. This 30mas object is possibly the Nuclear torus and/or a scattering halo. We discuss different contributions to the observed K band flux. Between 5GHz and the K-band the spectrum of this com- ponent is close to a 1=3 proportionality. In addition to the stan- dard interpretation of a hot dust torus surrounding the nucleus of NGC1068, one cannot exclude the possibility that a sizeable fraction of the Nuclearflux reaches us via a scattering halo. This then would allow us to determine physical parameters of the Nuclear Source.
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Diffraction-limited 76 mas Speckle Masking Observations of the Core of NGC 1068 with the SAO 6m Telescope
arXiv: Astrophysics, 1997Co-Authors: Markus Wittkowski, Yuri Balega, Thomas Beckert, Wolfgang J. Duschl, K.-h. Hofmann, Gerd WeigeltAbstract:We present the first K-band bispectrum speckle interferometry of NGC 1068 with an angular resolution of 76 mas (~5.5pc). This angular resolution allows us to attribute the measured flux to only one of the Nuclear Sources seen at radio wavelengths. The observed decreasing visibility function suggests that the dominant central core is probably not an unresolved point Source, but slightly resolved with a FWHM diameter of ~30 mas ~2pc for an assumed Gaussian intensity distribution. This 30 mas object is possibly the Nuclear torus and/or a scattering halo. We discuss different contributions to the observed K band flux. Between 5 GHz and the K-band the spectrum of this component is close to a nu^(1/3) proportionality. In addition to the standard interpretation of a hot dust torus surrounding the nucleus of NGC 1068, one cannot exclude the possibility that a sizeable fraction of the Nuclear flux reaches us via a scattering halo. This then would allow us to determine physical parameters of the Nuclear Source.
Fabien Grise - One of the best experts on this subject based on the ideXlab platform.
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a luminous x ray flare from the nucleus of the dormant bulgeless spiral galaxy ngc 247
The Astrophysical Journal, 2015Co-Authors: Hua Feng, Philip Kaaret, L Tao, Kazutaka Yamaoka, Shuo Zhang, Fabien GriseAbstract:NGC 247 is a nearby late-type bulgeless spiral galaxy that contains an inactive nucleus. We report a serendipitous discovery of an X-ray flare from the galaxy center with a luminosity of up to 2 x 10^(39) erg s^(−1) in the 0.3–10 keV band with XMM-Newton. A Chandra observation confirms that the new X-ray Source is spatially coincident with the galaxy nucleus. The XMM-Newton data revealed a hard power-law spectrum with a spectral break near 3–4 keV, no pulsations on timescales longer than 150 ms, and a flat power spectrum consistent with Poisson noise from 1 mHz to nearly 10 Hz. Follow-up observations with Swift detected a second flux peak followed by a luminosity drop by a factor of almost 20. The spectral and temporal behaviors of the Nuclear Source are consistent with the scenario that the flare was due to an outburst of a low-mass X-ray binary that contains a stellar-mass black hole emitting near its Eddington limit at the peak. However, it cannot be ruled out that the sudden brightening in the nucleus was due to accretion onto a possible low-mass Nuclear black hole, fed by a tidally disrupted star or a gas cloud; the Monitor of All-sky X-ray Image observations limit the peak luminosity of the flare to less than ~10^(43) erg s^(-1), suggesting that it is either a low-mass black hole or an inefficient tidal disruption event.
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a luminous x ray flare from the nucleus of the dormant bulgeless spiral galaxy ngc 247
arXiv: High Energy Astrophysical Phenomena, 2015Co-Authors: Hua Feng, Philip Kaaret, L Tao, Kazutaka Yamaoka, Shuo Zhang, Fabien GriseAbstract:NGC 247 is a nearby late-type bulgeless spiral galaxy that contains an inactive nucleus. We report a serendipitous discovery of an X-ray flare from the galaxy center with a luminosity up to 2*10^39 erg/s in the 0.3-10 keV band with XMM-Newton. A Chandra observation confirms that the new X-ray Source is spatially coincident with the galaxy nucleus. The XMM-Newton data revealed a hard power-law spectrum with a spectral break near 3-4 keV, no pulsations on timescales longer than 150 ms, and a flat power spectrum consistent with Poisson noise from 1 mHz to nearly 10 Hz. Follow-up observations with Swift detected a second flux peak followed by a luminosity drop by factor of almost 20. The spectral and temporal behaviors of the Nuclear Source are well consistent with the scenario that the flare was due to an outburst of a low-mass X-ray binary that contains a stellar-mass black hole emitting near its Eddington limit at the peak. However, it cannot be ruled out that the sudden brightening in the nucleus was due to accretion onto a possible low-mass Nuclear black hole, fed by a tidally disrupted star or a gas cloud; the MAXI observations limit the peak luminosity of the flare to less than ~10^43 erg/s, suggesting that it is either a low mass black hole or an inefficient tidal disruption event (TDE).
Jules P. Halpern - One of the best experts on this subject based on the ideXlab platform.
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New X-Ray Constraints on Starburst and Seyfert Activity in the Barred Spiral Galaxy NGC 1672
The Astronomical Journal, 2000Co-Authors: P. J. De Naray, W. N. Brandt, Jules P. Halpern, Kazushi IwasawaAbstract:The nearby barred spiral galaxy NGC 1672 shows dramatic starburst activity and may also host a Seyfert 2 nucleus. We present new X-ray observations that set constraints on starburst and Seyfert activity in NGC 1672. Two ROSAT HRI exposures, taken in 1992 and 1997, are used to investigate long-term variability of the known X-ray Sources and to search for new Sources of X-ray emission. We find large-amplitude (≈69%) variability from X-3, one of the off-Nuclear Sources located near an end of the galactic bar. X-3 has a peak observed 0.2–2.0 keV luminosity of ≈2.5 × 1039 ergs s-1, and it is probably a luminous X-ray binary or young supernova remnant. We do not observe variability of the Nuclear Source X-1 or the strong off-Nuclear Source X-2. Our analyses also reveal two new off-Nuclear Sources, one of which is associated with a bright region along a spiral arm, and we find evidence for large-scale diffuse X-ray emission throughout part of the disk of NGC 1672. Furthermore, we use ASCA data taken in 1995 to constrain the hard X-ray properties of NGC 1672. While the Nuclear Source X-1 is the dominant soft X-ray Source in NGC 1672, we find that the bulk of the 2–10 keV and 5–10 keV emission is spatially coincident with the off-Nuclear Source X-3, giving it an apparent 0.2–8 keV luminosity of 6 × 1039 ergs s-1. A power-law–plus–Raymond-Smith model provides an acceptable fit to the full-band ASCA spectra. We do not find any evidence for a luminous but absorbed Nuclear X-ray Source. If there is a luminous Seyfert 2 nucleus in NGC 1672, it must be obscured by a "Compton-thick" torus with a column density of 2 × 1024 cm-2.
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ROSAT PSPC and HRI observations of the composite starburst/Seyfert 2 galaxy NGC 1672
Monthly Notices of the Royal Astronomical Society, 1996Co-Authors: W. N. Brandt, Jules P. Halpern, K. IwasawaAbstract:The nearby barred spiral galaxy NGC 1672 has been observed with the Position Sensitive Proportional Counter (PSPC) and High Resolution Imager (HRI) instruments on board the ROSAT X-ray satellite. NGC 1672 is thought to have an obscured Seyfert nucleus, and it has strong starburst activity as well. Three bright X-ray Sources with luminosities 1-2 x 10(exp 40) erg/s are clearly identified with NGC 1672. The strongest lies at the nucleus, and the other two lie at the ends of NGC 1672's prominent bar, locations that are also bright in H alpha and near-infrared images. The Nuclear Source is resolved by the HRI on about the scale of the recently identified Nuclear ring, and one of the Sources at the ends of the bar is also probably resolved. The X-ray spectrum of the Nuclear Source is quite soft, having a Raymond-Smith plasma temperature of approximately equals 0.7 keV and little evidence for intrinsic absorption. The ROSAT band X-ray flux of the Nuclear Source appears to be dominated not by X-ray binary emission but rather by diffuse gas emission. The absorption and emission properties of the Sources, as well as their spatial extents, lead us to models of superbubbles driven by supernovae. However, the large density and emission measure of the Nuclear X-ray Source stretch the limits that can be comfortably accommodated by these models. We do not detect direct emission from the putative Seyfert nucleus, although an alternative model for the Nuclear Source is thermal emission from gas that is photoionized by a hidden Seyfert nucleus. The spectra of the other two X-ray Sources are harder than that of the Nuclear Source, and have similar difficulties with regard to superbubble models.
Kazushi Iwasawa - One of the best experts on this subject based on the ideXlab platform.
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New X-Ray Constraints on Starburst and Seyfert Activity in the Barred Spiral Galaxy NGC 1672
The Astronomical Journal, 2000Co-Authors: P. J. De Naray, W. N. Brandt, Jules P. Halpern, Kazushi IwasawaAbstract:The nearby barred spiral galaxy NGC 1672 shows dramatic starburst activity and may also host a Seyfert 2 nucleus. We present new X-ray observations that set constraints on starburst and Seyfert activity in NGC 1672. Two ROSAT HRI exposures, taken in 1992 and 1997, are used to investigate long-term variability of the known X-ray Sources and to search for new Sources of X-ray emission. We find large-amplitude (≈69%) variability from X-3, one of the off-Nuclear Sources located near an end of the galactic bar. X-3 has a peak observed 0.2–2.0 keV luminosity of ≈2.5 × 1039 ergs s-1, and it is probably a luminous X-ray binary or young supernova remnant. We do not observe variability of the Nuclear Source X-1 or the strong off-Nuclear Source X-2. Our analyses also reveal two new off-Nuclear Sources, one of which is associated with a bright region along a spiral arm, and we find evidence for large-scale diffuse X-ray emission throughout part of the disk of NGC 1672. Furthermore, we use ASCA data taken in 1995 to constrain the hard X-ray properties of NGC 1672. While the Nuclear Source X-1 is the dominant soft X-ray Source in NGC 1672, we find that the bulk of the 2–10 keV and 5–10 keV emission is spatially coincident with the off-Nuclear Source X-3, giving it an apparent 0.2–8 keV luminosity of 6 × 1039 ergs s-1. A power-law–plus–Raymond-Smith model provides an acceptable fit to the full-band ASCA spectra. We do not find any evidence for a luminous but absorbed Nuclear X-ray Source. If there is a luminous Seyfert 2 nucleus in NGC 1672, it must be obscured by a "Compton-thick" torus with a column density of 2 × 1024 cm-2.
